Electric furnace



March 27, 1928.

Y I. RENNERFELT ELECTRIC FURNACE Filed Aug. 18. 1926 InvencoY: fwrr m /w:

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Patented Mar. 27, 1928.

UNITED STATES IVAR RENNEBFELT, F DJURSHOLM, SWEDEN.

ELECTRIC FURNACE.

Application filed August 18, 1926, Serial No. 129,961, and in Sweden September 1, 1925.

My invention relates particularly to electric furnaces employing metallic resistors for generating the heat, and it has for its objects: First, to provide a furnace capable of operating at a very high temperature;

second, to provide means for obtaining a fairly uniform temperature; third, to facilitate assembling of the furnace; fourth, to cheapen the construction by using a multiple-unit system for building up the furnace chamber; fifth, to facilitate removal or exchange of the heating resistors and, sixth, to provide means for securely, yet yieldingly, fastening the heating resistors to the walls of the furnace chamber.

I attain the objects enumerated above by providing a furnace having a heating chamber made up of a plurality of heating elements, each consisting of a preferably unitary, flat frame or ring of refractory material, which on the inside edge is carrying the heating resistor, which may consist of a flat ribbon, a straight wire, a coil or spiral of wire or of any kind of a metallic resistor, which may be used in electric heating ovens.

Each heating element may be considered as a transversal section of the furnace chamber, the number of the elements being determined by the length of the heating chamber, the number of phases and the amount of heat to be generated. The heating element is made up of refractory bricks-or plates, assembled in a frame of iron or any other suitable metal, and preferably provided with a groove in the edge, which is turned inwards, so as to afford a certain protection to the resistor, being placed in said groove.

The resistors are made up of turns, surrounding the entire heating chamber, each heating element carrying one or preferably several in series, as this means fewer terminal leads and, thus, a higher thermal e'lficiency. The terminals belonging to each turn or series of turns are brought out to the outsid of the furnace in a plane paraliei to the fiat frame or ring, support ing the resistors, and are then connected to a l board in any desired manner.

A to use flat, rather thin ribbons i for gener the heat and to locate them with the Wt side towards the furnzice wall so as an unobstructed radiation of us the interior of the furnace.

By a am aide to operate the furnace with only a smaii erence in the temperature of the waging theresistors in this way preferred manner. The ribbons may f. i. be

kept in place by means of clamps of the same ribbon material, surrounding the resistor and secured to certain places of the refractory body, constituting the heating unit. For this purpose small rivets or nails of the same material as the resistor itself may be used, which are introduced into holes in the refractory material and fastened to this in any suitable way.

The invention is not limited to any certain shape of the refractory frames, which may becircular, rectangular or of any other form as required for the furnace chamber.

The resistors may, furthermore, be divided into parts of a complete turn around the inside furnace wall, each part having its two terminal leads on opposite places and not near each other as in the case of the resistors forming complete turns around the inside.

The accompanying drawing shows in two vertical sections a furnace embodying the principal features of my invention.

Fig. 1 shows a rectangular frame at the lines XX in Fig. 2, which represents a vertical section at the lines YY in Fig. 1.

A resistor in the shape of a ribbon is indicated by 1 and a refractor body, supporting the ribbon, by 2. This ody is made up of a plurality of suitably shaped bricks, heid together by means of an. iron hoop 3, so as form a selfcontained unit. By placing severai M such units adjacent to each other iarnace chamber of any desired iength built up, having square, oval or round cross sec- 'tion as the case may be. The resistor i connected to the power suppiy by means terminals 1-, proiecting through the e at e places icated weii i dated cm the iron hoop, whic hoids "the several =Ciamps a by 6. Said rial. The resistors ma also be fastened by means of Wires or ban 9,surrounding the resistors and also a part of the refractory body, which may have holes 10, intended to receive the bands 9. Grooves 11 may be provided in the refractory body in order to af ford protection to the resistors. The object to be' heated may be of heat resisting material, which may be developed into a muffle.

The system of heating elements making up the furnace chamber may be surrounded by a steel plate shell in any preferred manner. This outside shell is not shown on the drawing, as it is more or less immaterial to the invention.

The heating elements as described above may be used in furnaces having a horizontal heating chamber as well as in furnaces having a vertical chamber, in which f. i. a crucible ma be located for melting anything not requiring a temperature above 1150 or thereabout.

Having now fully described my invention, 1 claim and desire to secure by Letters Patent of the United States:

1., In an electric furnace a refractory, frame shaped flat bod a ribbon resistor located concentrically a ong the inner edge of the body, and means for securely clamping and reinforcing the body on the outside edge. I

2. In an electric furnace the combination of a refractory body in the shape of a flat frame with a resistor, preferably in the shape of a ribbon, straight and securely atplaced on a plate 12' neeaiea tached to the said body concentrically along the inner edge of the refractory body, and located in a protecting groove, which project inwards beyond the resistor,

the walls of 1 the ends of which are brought out of the furnace at right angles to the longitudinal axis of same.

3. In an electric frame shaped flat body, cated concentrically along furnace a refractory,

a ribbon resistor 10- the inner edge of the body and means for securely clamping bodies, having heating resistors straight and securely attached concentrically along the inner edges, the ends of each resistor being brought out of the furnace at right angles to the longitudinal axis of same.

5. In an electric furnace a frame-sha ed, refractory fiat body in combination wit a heating resistor located concentrically along the inner edge of the body and securely attached to the body by means of clamps which are in any suitable manner secured to the body, the ends of the resistor being brought out of the furnace at right angles to the longitudinal axis of same.

Signed at Stockholm in the county of Stockholm Lan and State of Sweden this 6th day of August A. D. 1926.

' IVAR' RENNERFELT. 

